[Regulation of corticotropic function in stressful situations]

ACTH secretion is mainly controlled by two hypothalamic neurohormones: corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP). Both peptides are synthesized in the hypothalamic paraventricular nucleus (PVN) (in parvo-cellular neurons for CRH and in magnocellular neurons for most AVP). Under basal conditions, some CRH neurons coexpress AVP (CRH+/AVP+ neurons). This colocalisation represents a form of functional plasticity since the number of CRH+/AVP+ neurons increases after acute or repeated stress exposure. Experiments in sheep and rat (studies on the secretion of both peptides in hypophysial portal blood, effects of anti-CRH and anti-AVP immunisation upon ACTH secretion) indicate that stress-induced ACTH stimulation involves both CRH and AVP. Unlike CRH which participates also in the maintenance of basal ACTH and glucocorticoids secretion, the role of AVP appears to be limited to corticotropic response to stress.